Projection lamp



y 14, 1968 R. F. SCOLEDGE ETAL 3,383,539

PROJ ECT ION LAMP Original Filed Feb. 1. 1960 VOLTAGE FOE RATED LIFE STUART S. DAVlS ROBERT F SCOLEDGE IN V EN TORS Wig-4 ATTORNEY United States Patent 3,383,539 PROJECTION LAMP Robert F. Scoledge, Danvers, and Stuart S. Davis, Lynn, Mass., assignors to Sylvania Electric Products Inc., a corporation of Delaware Continuation of appiication Ser. No. 413,581, Nov. 24, 1964, which is a continuation of application Ser. No. 5,867, Feb. 1, 1960. This application Feb. 6, 1967, Ser. No. 614,785

1 Claim. (Cl. 313-113) This is a continuation of copending application Ser. N0. 413,581, filed NOV. 24, 1964, which in turn is a continuation of application Ser. No. 5,867 filed Feb. 1, 1960 both of which were abandoned.

This invention relates to incandescent lamps for projection purposes, that is, for projecting a beam of light. Such lamps are used, for example, in moving picture and slide projectors. In their most recent forms, such lamps include a metallic reflector in close proximity to an incandescent filament which has the form of a coiled-coil.

The most efficient form of coil for such lamps has been found to be one that operates at between about and 23 volts, and particularly at about 21.5 volts, and that a coil designed for a voltage greater or smaller than that will not be as efficient. Efliciency in such lamps is a factor of great importance because a high efficiency means that a given amount of light is produced at a lower watt input to the lamp, thereby causing less heating effect on the film or slide and requiring a smaller blower for cooling the lamp.

We have discovered that the efficiency of the coil can be further increased by pulling out one turn on each side of the coil between the main coil and the supporting leadin wires. This appears to reduce the temperature gradient along the ends of the coil, thereby reducing preferential etching due to the temperature gradient.

In addition, it facilitates control of the total effective filament length by insuring that said length is terminated at a particular turn. The end turns of the filament, beyond the pulled-out turn, have a mandrel or so-called spud inside them, thereby both short-circuiting them and facilitating their attachment to a support wire. The mandrel or spud terminates at about the middle of the axial length of the pulled-out turn and insures that the termination occurs at that particular turn, and not one on either side of it, as could easily be the case if the mandrel were inserted into the closely-wound coil without the pulled turn. The importance of fixing the exact turn at which the effective length of the coil terminates (that is, the turn at which the shorting effect of the spud begins) is indicated by the fact that a variation of one turn can make a life difference of 7%.

The projection lamp is generally designed for vertical operation with the base down, that is, with the base at the bottom. If the lead-in Wires to the filament extend transversely to the lamp axis in the region in which the filament is attached to them, we have discovered that having the legs of the filament extend outward from the top of the coil, that is, from the part of the coil furthest from the base, rather than from the axis of the coil, or the bottom or side, the operation is much better. We find that, under such circumstances, the sag in the turn will bend them outward from each other and not closer together, thereby preventing short-circuiting or overheating. The legs of the coil are preferably attached to the top of the lead-in wires.

Other advantages, features and objects of the invention will be apparent from the following specification, taken in connection with the accompanying drawing in which:

FIGURE 1 is a profile view, partly in section, of one embodiment of a lamp according to the invention;

FIGURE 2 is a front view of the same lamp;

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FIGURE 3 is an enlarged view, partly in section, of the structure of the filament and its supports;

FIGURE 4 is a graph showing the variation in light output with filaments of different voltages, and

FIGURE 5 is an enlarged view, partly in section, of the filament as it sags in operation.

In FIGURE 1, an enclosing tubular glass envelope 1 contains the incandescible coiled filament 2 and the polished metal reflector 3 in position to reflect light from said filament. The reflector can be parabolic, with the filament substantially at the focus, if a parallel beam of light is desired; but for use in a slide or motion picture projector, the reflector is generally made elliptical, with the filament at the near focus of the ellipse.

The reflector and filament are made in a unitary structure, with the lead-in wires 4, 5 which support the filament extending through a ceramic insulating bushing 6 fixed to reflector 3 through an opening therein. In this way, the filament and reflector can be fixed in position with respect to each other before being fixed in position in the envelope 1. The latter has four stiff wire contact prongs7, 8, 9 (the one which would be 10 is not shown) sealed through the bottom or base 11 of the envelope 1.

A metal cap 12 fits around the base 11, extending up the cylindrical wall 13 of envelope 1 and containing the downwardly-extending hollow projection 14, which protects the sealed exhaust tube 15. Each contact prong 7, 8, 9 (and 10 not shown) has the glass beads 16, 17, sealed around it, and the metal cap 12 has holes through which said beads pass.

The cap 12 carries three spaced projections 19, 20, 21 which cooperate with fingers in a socket to align the bulb therein. One said socket is shown in copending application Ser. No. 553,337, filed Dec. 15, 1955, by William H. Morgan, Jr. for a Lamp Positioner. The projection 14 has the key 22 as shown in FIG. 2 extending parallel to the axis of the envelope, to aid in aligning the lamp in a socket.

The lead-in wires 4, 5 extend directly only a short distance behind the bushing 6, the connecting wire 12 being connected to wire 4 at the back of bushing 6 and extending downward at an angle to be connected near its end to lead-in wire 8. The connecting wire 12 is bent crosswise to lead-in wire 8 to make a more effective supporting connection. Lead-in wire 10, not shown, would be similarly connected to a support wire 18 between lead-in wire 5 and a contact prong.

The reflector 2 has two eyeletted tabs 23, 24, and a short support wire 25, 26 is welded across the tab and welded also to the contact prongs 7, 9. This helps align the reflector in the bulb and keeps it in position.

By running the lead-in wires 4, 5 through closelyfitting holes in the ceramic backing 6, arcing between the lead-in wires on filament burnout is prevented, and a fuse to prevent such arcs is unnecessary. The narrow hole through which the arc must pass in the ceramic 6 snutfs it out.

The filament 2 and its supports, 4, 5 are shown in more detail in FIG. 3. The supporting wires 4, 5 extend through the ceramic bushing 6 and are bent outwardly as they emerge from said bushing on the concave side of the reflector. This bending together with the welding of connecting wires 12, 18 to lead-in wires 4, 5 at the other end of the ceramic 6 helps keep the filament and reflector in permanent alignment.

The filament 2 itself is a coiled-coil having a tungsten wire 27 coiled into a primary coil 28 of small diameter, with the middle length of the primary coil being itself again coiled to form a coiled-coil 29 of larger diameter. The turns 30 and 31 are pulled out to a greater distance than the remainder of the coil, for reasons previously explained. Each end portion 32, 33 of the coil has a mandrel 34, generally called a spud, fitted tightly inside it to facilitate welding or other connection to the lead'in wires 4, 5 and also to short the ends of the coil to keep them from being heated as much as the remainder of the coil. For convenience in drawing, the spud is terminated at the beginning of the pulled-out turn, but in practice it will be desirable to have it near the middle of the turn, so that variations in the exact amount of insertion will not have much effect.

As an example of a coil according to the invention, the portion 32 would be about 6 turns long, and the portion 28 would be about 8 turns long, with five secondary turns in the coiled-coil portion 29. The latter portion has 30 turns per inch, and the spud 34 is a tungsten pin 0.030 inch in diameter. The primary coil was wound to 64 turns per inch on a l0-mil mandrel. The average primary coil diameter was 26.7 mils.

In the specific embodiment here described, the reflector had an elliptical curvature according to the following curve where y is the vertical coordinate and x the horizontal coordinate when the reflector is positioned in the bulb as shown in FIG. 1 and the base is down, that is, at the bottom of the envelope.

The side of the coiled-coil filament nearest to the reflector is positioned 0.070 inch in front of the plane of the outer edges 34, 35 of the reflector, and that plane is 0.450 inch from the apex of the reflector, that is, from the apex of the reflector curve where it would pass through ceramic 6 if that ceramic were not there.

In operation, a voltage of about 21.5 volts is connected between the filament contact prong 8 and the corresponding prong (not shown) to the other side of the filament. the contact prongs 7 and 9 are left floating, that is not connected to anything because if they are connected to either side of the line, the reflector will blacken by conduction through the gas to the other end of the voltage supply line.

The graph of FIG. 2 shows the lamp efliciency in lumens per watt (L.P.W.) at the screen of a projector, plotted against the voltage at which the filament must be operated to obtain the rated life of 15 hours. (The life in a projector lamp is customarily of that value in order to obtain high efliciency.) The filaments used were different for each voltage, but the wattage and overall dimensions of the filament were the same.

In other words, a series of filament coils were made,

each coil being of 0.200 inch axial length and 0.085 inch 0 The lumens per watt at the screen on which the lens was focussed were then measured.

In that way, the best coil for efficiency was found to be one that gave the rated life at 21.5 volts. All other coils were less etficient.

When the coil is designed for a voltage of about volts or more, it can no longer be made of such dimensions as to fit within the 0.200 inch by 0.085 inch dimensions given above, and a coil for direct operation on a -volt line will have only about sixty percent of its turns within a rectangle of the dimensions given above. The light from the remaining turns will therefore not be useful in filling the usual projection lens with which the lamp would normally be used.

The tungsten wire of which the coil is wound had, in the specific example cited earlier in the present application, a diameter of about 8.48 mils. When wound in the manner described, the finished coiled-coil will have a diameter of about 0.85 inch.

What we claim is:

1. An incandescent projection lamp comprising a sealed enclosing envelope, support wires in said envelope, a reflector inside said envelope, and a filament in reflecting relationship to said reflector, said filament comprising a coil having a spud therein at the ends only of said coil, the turn of said coil at the inside ends of said spud being stretched out so that part of it is in contact with said spuds and part of it beyond said spud, the portion of the coil having the spud therein having their longitudinal axes substantially in line with each other, the filament coil being supported solely by said spud, an end of each coil with a spud therein being affixed perpendicularly to a support wire, the support wires being sealed through said envelope at one end thereof, and the portions of the coil having the spuds therein being in line with the top of the coil, the top being taken as the part opposite to that nearest the end of said envelope through which the support wires are sealed, the pulled out turn being in line with the spuds and extending to legs of the coil also in line with each other, whereby any sag in the turns of the coil will bend them outward from each other and thereby prevent short-circuiting.

References Cited UNITED STATES PATENTS 1,637,034 7/1927 Bergmans 313-279 X 2,404,992 7/1946 Stone 313-279 X 2,848,642 8/1958 Wisco et a1. 3113-344X 2,980,818 4/1961 Harris et al. 313-l 13 HERMAN KARL SAALBACH, Primary Examiner.

GEORGE N. WESTBY, Examiner.

S. CHATMON, JR., Assistant Examiner. 

1. AN INCANDESCENT PROJECTION LAMP COMPRISING A SEALED ENCLOSING ENVELOPE, SUPPORT WIRES IN SAID ENVELOPE, A REFLECTOR INSIDE SAID ENVELOPE, AND A FILAMENT IN REFLECTING RELATIONSHIP TO SAID REFLECTOR, SAID FILAMENT COMPRISING A COIL HAVING A SPUD THEREIN AT THE ENDS ONLY OF SAID COIL, THE TURN OF SAID COIL AT THE INSIDE ENDS OF SAID SPUD BEING STRETCHED OUT SO THAT PART OF IT IS IN CONTACT WITH SAID SPUDS AND PART OF IT BEYOND SAID SPUD, THE PORTION OF THE COIL HAVING THE SPUD THEREIN HAVING THEIR LONGITUDINAL AXES SUBSTANTIALLY IN LINE WITH EACH OTHER, THE FILAMENT COIL BEING SUPPORTED SOLELY BY SAID SPUD, AN END OF EACH COIL WITH A SPUD THEREIN BEING AFFIXED PERPENDICULARLY TO SUPPORT WIRE, THE SUPPORT WIRES BEING SEALED THROUGH SAID ENVELOPE AT ONE END THEREOF, AND THE PORTIONS OF THE COIL HAVING THE SPUDS THEREIN BEING IN LINE WITH THE TOP OF THE COIL, THE TOP BEING TAKEN AS THE PART OPPOSITE TO THAT NEAREST THE END OF SAID ENVELOPE THROUGH WHICH THE SUPPORT WIRES ARE SEALED, THE PULLED OUT TURN BEING IN LINE WITH THE SPUDS AND EXTENDING TO LEGS OF THE COIL ALSO IN LINE WITH EACH OTHER, WHEREBY ANY SAG IN THE TURNS OF THE COIL WILL BEND THEM OUTWARD FROM EACH OTHER AND THEREBY PREVENT SHORT-CIRCUITING. 